2>2,2 



NATURE 



[June 26, 1919 



10,000 gauges were dealt with in this building alone. 

 A minimeter of special design was shown which en- 

 abled rapid and accurate measurements to be made 

 on slip-gauges. The instrument serves to indicate the 

 difference between the gauges under test and the 

 corresponding standard gauges kept at the laboratory. 

 A difference as small as one millionth o\ an inch is 

 readily shown on the scale of the instrument. The 

 following instruments for measuring and inspecting 

 screw-gauges were exhibited : — (i) Screw diameter- 

 measuring machines of the "floating micrometer 

 type," (2) screw-pitch measuring machines for check- 

 ing accuracy of pitch of screw-gauges, and (3) vertical 

 projection apparatus giving a magnification of 50. 

 Errors of 0000 1" in the thread form can be detected 

 with this instrument. 



The exhibits of the optics division included the 

 following : — A large Michelson interferometer, as 

 modified by Twyman, for testing prisms and lenses ; 

 another interferometer used for determining the 

 planeness of flat surfaces and the parallelism of glass 

 plates, on which measurements could be made to 

 within a tenth of an interference fringe ; the following 

 methods for the accurate determination of the curva- 

 tures of lens surfaces — (a) a magnification method for 

 very steep curves such as are encountered in micro- 

 scojpe objectives, (b) the Guild precision spherometer 

 for medium curves, and (c) an arrangement of Newton 

 rings for shallow curves, either convex or concave ; a 

 simple projection apparatus for testing mirrors for 

 defects in polishing, silvering, or in quality of the 

 glass ; and apparatus for testing blocks of prisms 

 for strain. 



The heat division showed an apparatus for testing 

 the heat-insulating properties of materials employed 

 in the construction of cold stores, an apparatus for 

 detecting contaiitinated regions in thermo-elements, 

 and an instrument (designed by Mr. E. A. Griffiths) for 

 indicating the contents of the petrol tank of aircraft 

 or automobiles. The latter works on the principle 

 that the heat loss from a wire is greater when the 

 wire is immersed in a liquid than when exposed to 

 air or vapour. The instrument is compensated for the 

 effect of varying atmospheric temperatures. 



The exhibits of the electricity department included 

 apparatus for the accurate measurement of capacity 

 at low frequencies ; an electrical method of measuring 

 frequency; apparatus for measuring the amplifying 

 power of valves at audible frequency ; the reception of 

 continuous Waves by the heterodyne method ; and a 

 three-electrode valve set for producing oscillations of 

 telephonic frequency. 



The working of the Paterson-Walsh electrical 

 height indicator was demonstrated. This instrument 

 consists of two observation tubes capable of rotation 

 about parallel axes placed at a known distance apart. 

 The two parts are electrically connected, and the con- 

 nections are so arranged that the height of the object 

 is given directlv on a dial attached to the apparatus. 

 Other items of interest shown were the methods of 

 testing radium dials, the testing of insulators for high- 

 voltage transmission under artificial rain, arc lamps 

 for searchlights, and the heating of buried cables. 



PHYSIOLOGY OF SEX AND REPRO- 

 DUCTION IN POULTRY. 



TN numerous animals it seems that the determina- 

 ■■• tion of sex depends upon the chromosome content 

 of the egg-cell and sperm-cell. But there is consider- 

 able evidence that in some cases the normal sex-ratio 

 may be experimentally modified and in some degree 

 controlled. This led Prof. Raymond Pearl (Proc. 

 Amer. Phil. Soc, vol. Ivi., 1917, pp. 416-36) to make 



NO. 2591, VOL. 103] 



a statistical investigation of the sex-ratio in the 

 domestic fowl, and he considers data representing 

 22,000 chicks. In families of ten and more Prof. Pearl 

 found the ratio of males per 1000 females to be 944, 

 or 4857 per cent. ; and it is very interesting to notice 

 the nearly perfect agreement of this result with 

 Darwin's, which was 4864 per cent. There is normal 

 variability from stock to stock and from year to year, 

 and aberrant sex-ratios occur. But before these 

 aberrant sex-ratios can be regarded as indicative of 

 either environmental or hereditary effects, it is neces- 

 sary to show that they occur with such frequency as 

 to exceed considerably the frequency expected on the 

 basis of chance alone. This has not been done. In 

 regard to the flocks Prof. Pearl dealt with, there was 

 evidence that the pre-natal mortality is not differential 

 in respect to sex. It follows that the sex-ratio ob- 

 served at birth is substantially the same as the initial 

 zygotic sex-ratio — that is to say, the ratio determined 

 by the constitution of the fertilised ovum. In another 

 paper {Science, vol. xlvi., 1917, p. 220) Prof. Pearl 

 states that hens with high fecundity as a fixed charac- 

 teristic tend to produce a larger proportion of female 

 offspring — a very important conclusion. 



For measuring the net reproductive ability of mated 

 pairs of the domestic fowl (Barred Plymouth Rocks) 

 Prof. Pearl proposes (Genetics, 1917, pp. 417-32) a 

 reproductive or fertility index. This index expresses 

 the actual number of chicks produced by the mating 

 and capable of living three weeks after hatching as a 

 percentage of the maximum total number of chicks 

 which it would be physiologically possible for the 

 mating to produce. It has a mean value of about 

 12 per cent. Net fertility, as measured by the repro- 

 ductive index, is a rather highly variable character, 

 agreeing in this respect with other purely physiological 

 characters. i\s to the influence of age, it is shown 

 that reproductive ability, as measured by the index, 

 diminishes with advancing age of the birds mated, 

 having its maximum when each of the birds mated 

 is from ten to fourteen months old. The rate of 

 decline v.'ith advancing age is more rapid in the males 

 than in the females. 



In mammals there is a steady increase in the rate 

 of fertility to a maximum, after which, with a further 

 increase in age, there is a decline to total sterility. 

 But in the fowls Prof. Pearl experimented with there 

 is a steady and progressive decline in fertility after 

 the first breeding season (Proc. Nat. Acad. Sci., 

 vol. iii., 1917, pp. 354-56). There is a significant 

 drop in reproductive ability as we pass from a com- 

 bined age of two years for the mated birds to three 

 years. In passing from three years to four there is no 

 significant change. In passing from a combined age 

 of four years to five there is a large drop in the net 

 reproductive ability of the mating. 



Miss Alice M. Boring and Prof. Pearl discuss 

 (Anat. Record, vol. xiii., 1917, pp. 253-68, 6 figures) 

 the extraordinarily discrepant statements that are 

 made in regard to the presence or absence of inter- 

 stitial cells in the testes of male birds. They find 

 these elements in the testes of just hatched chicks. 

 But they may be, and usually are, quite absent from 

 the testes of birds more than six months old and of 

 full sexual maturity as regards both primary and 

 secondary characters. This makes it difficult to 

 believe that the interstitial cells of the testes have (in 

 the case of the fowl) any causal influence upon the 

 secondary sex-characters. The observers found true 

 interstitial cells invariably present in the ovary, and 

 they notice that these elements are structurally iden- 

 tical in the two sexes. 



In a joint paper (Amer. Journ. Anat., vol. xxiii., 

 1918, pp. 1-35, 9 plates, 6 figures) Prof. Pearl and 



